This means that he lacked sufficient course content in his bachelor's degree to enable him successfully pursue the master's program that he applied to. Universities usually check the content of your undergraduate course to confirm if you have earned a sufficient number of credits in relevant areas. If you haven’t, they deem you ineligible to pursue their master's program.
I will advise him to apply to a masters program that is related to his bachelors next time. For instance, the fact that he has a bachelors in engineering physics doesn’t mean he can apply to a masters program in let’s say electrical engineering in Germany. He might lack some crucial subjects that will make understanding some concepts in an electrical engineering masters degree very difficult.